Curable, or thermosettable, coating compositions are widely used in the coatings art, particularly for topcoats in the automotive and industrial coatings industry. Color-plus-clear composite coatings are particularly useful as topcoats for which exceptional gloss, depth of color, distinctness of image, or special metallic effects are desired. The automotive industry has made extensive use of these coatings for automotive body panels.
Single-layer topcoats and the clearcoats of color-plus-clear composite coatings, however, require an extremely high degree of clarity and gloss to achieve the desired visual effect. Such coatings also require a low degree of visual aberrations at the surface of the coating in order to achieve the desired visual effect such as high distinctness of image (DOI). As such, these coatings are especially susceptible to a phenomenon known as environmental etch. Environmental etch manifests itself as spots or marks on or in the finish of the coating that often cannot be rubbed out. It is often difficult to predict the degree of resistance to environmental etch that a high gloss topcoat or color-plus-clear composite coating will exhibit. Many coating compositions known for their durability and/or weatherability when used in exterior paints, such as known high-solids enamels, do not provide the desired level of resistance to environmental etch when used in high gloss coatings such as the clearcoat of a color-plus-clear composite coating.
Curable coating compositions utilizing carbamate- or urea-functional materials are described, for example, in U.S. Pat. Nos. 5,756,213; 5,760,127; 5,770,650, 5,792,810; and 5,827,930, each of which is incorporated herein by reference. These patents describe coating compositions including a carbamate-functional or urea-functional compound prepared by a ring-opening reaction with a lactone. While such compounds have proven useful in coatings, particularly coatings for flexible substrates, it has been found that even a modest number of lactone units in the compounds give rise to problems of solidification during storage at room temperature and the need to employ higher amounts of solvent than desired in order to obtain suitable viscosities. On the other hand, decreasing the average number of lactone units per compound leads to less than optimum properties in the cured coating, such as poorer durability, less resistance to environmental etch, and less resistance to scratching and marring.